There has long been known in the art a method of manufacturing booklets that comprise a bundle of sheets, for instance paper sheets, and a casing includes providing the casing with a spine and applying to the inner surface thereof a binding agent in the form of a deactivated glue. The bundle of sheets is inserted into the casing such as to bring one side edge of the bundle into abutment with the glue on the casing spine. The casing is normally comprised of cover sheets that form a front side and a back side which are connected to the spine, said front and back covers having essentially the same shape and size as the sheets in said bundle. The casing may also be made of paper, although it can, of course, be made of any other suitable material.
When the bundle is in place in the casing, the glue on the spine of the casing is activated so as to firmly glue the bundle to the spine, along one of the side edges of said bundle. This can be achieved, for instance, by initially applying the glue in a solid state and then heating the glue so as to bring it to a liquid or semisolid state. In this regard, one side edge of each sheet in the bundle is in contact with the glue. The glue is then allowed to cool to a solid state, therewith fastening the bundle of sheets to the spine of the casing.
When a large number of booklets are to be produced, it is known to automate the whole of the manufacturing process or parts thereof. Thus, apparatus are known by means of which manufacture can be automated. It is known to use in such arrangements or plants conveyors that transport a casing to a gluing station from a compilation station in which a sheet bundle is inserted into said casing. In this known arrangement, the gluing station includes a conveyor by means of which a plurality of booklets are moved singly and sequentially in a transportation direction that is generally perpendicular to the plane of each booklet. The booklets are therewith moved over a glue-activating unit, where the spine of each booklet is moved in the close proximity of a heating element, so as to melt the glue. In the case of this known arrangement in which the sheet bundle rests with one of its side edges against the spine of the casing, the side edges penetrate slightly into the glue as a result of the gravitational force acting on the bundle. Each booklet is then allowed to cool, so as to unite said bundle with the casing and therewith obtain a finished booklet.
The known conveyor includes two dogging devices, each having a plurality of dogging yokes. The conveyor-carried dogging yokes are moved along the glue-activating unit in the transporting direction. Each booklet arriving at the glue-activating unit is positioned with a pair of dogging yokes on each dogging device straddling two mutually opposing side edges of the booklet. In order to enable the booklet to be inserted between the two pairs of dogging yokes, the latter are spaced apart at a distance which is greater than the thickness of the booklet, so that straddling can take place with a relatively large clearance in the transport direction. Because the arrangement shall be able to deal with booklets of mutually different thicknesses, the distance between mutually adjacent dogging yokes is adapted so that the clearance provided will be sufficient to accommodate booklets of relatively large thickness. The clearance can therefore be relatively large in respect of the manufacture of thinner booklets. This is necessary in order to be able to place a booklet readily and securely in conveyors, particularly when it is automated as in the case of the known arrangement. A booklet manufacturing apparatus of this kind is described in WO91/04159, for instance.